W22 PEGylation: Making "Stealth" drugs Flashcards
What are protein and peptide drugs?
- Protein drugs: active substances made up of essential amino acids (>50 AAs)
- Peptide drugs: active substances made up of essential amino acids (<50 AAs)
Peptide drug classes mostly consist of hormones, e.g. insulin, human growth hormone
There are only two orally active peptide
drugs on the market: ciclosporin &
desmopressin
What are two principal drug delivery issues?
- Stability on storage
- In vivo delivery (Hydrolysis of peptide bond, High MW hindering absorption)
- But even when administered via the intravenous route there is the issue of clearance
The problem with protein drugs?
- Even when proteins do reach the systemic circulation (the i.v. route being common) they are rapidly eliminated from the blood
- Renal excretion
- Opsonisation = capture in the liver (and by macrophages)
- Generation of neutralising antibodies, i.e. immunogenic response
- Proteolysis
Physiological half-lives (t½) of protein/ peptide drugs can be short;
Short half-lives are a problem if a drug needs to be injected
How can we ‘hide’ the drug? (2 approaches)
What are these referred to as?
Approach 1: Large MW polymer covalent;y added to the protein
Approach 2: Multiple lower MW polymer covalently added to the protein
Both of these approaches are referred to as creating a “halo effect”
Covalent attachment= creates a new (higher MW) macromolecule
Hiding the drug:
What are the physiological benefits?
- The end result of both approaches is a higher MW macromolecule, but where the protein component is shielded by the polymer
This has the following physiological benefits:
- Higher MW reduces glomerular filtration rate so reduces renal excretion
- Polymer shields protein from proteases in the blood slowing hydrolysis
- Opsonisation (adsorption of plasma proteins) is reduced = reduced elimination via the liver or macrophages
- Polymers employed are non-immunogenic
Overall effect is reduced clearance and longer physiological half-life (t½) of the drug
What polymer can be used?
What are the ideal properties required for hiding drugs? (6)
- Biocompatible i.e. non-toxic
- Lacks immunogenicity
- Water soluble
- Mobile and highly hydrated to create a “halo” around the protein
- Easy to attach to proteins
- Readily cleared from the body after metabolism of the attached protein
What is PEG?
Properties?
- Polyethylene glycol
- A synthetic, linear homopolymer
- Water-soluble, biocompatible, well-tolerated and FDA approved
- PEG has become the gold standard polymer in the bio conjugation of protein drugs
In the 1970s Professor Frank Davis pioneered the bioconjugation of proteins with polyethylene glycol (PEG)
PEGylation:
- High MW protein will often require the attachment of several PEG molecules (40-50 KDa)
- PEG molecules also become heavily hydrated – 2 or 3 H2O molecules per monomer unit = effectively increases the MW
- Attachment of PEG molecule(s) has been shown to slow renal clearance, proteolysis and opsonisation of many protein drugs
- BUT… PEGylation near the active site of the
protein could reduce the efficacy
Attachment site should be away from the active site of the protein
Rheumatoid arthritis & TNF-a
What is RA?
What is important in the pathogenesis of RA?
- RA is a chronic inflammatory disease
- It is an autoimmune disorder, i.e., the immune system mistakenly attacks its own body
- The pro-inflammatory cytokine TNF-α has been shown to be important in the pathogenesis of RA
- TNF-α inhibitors have been developed and
are proving effective in the treatment of RA - To understand TNF-α inhibitors we need to
understand monoclonal antibodies (MABs) - MABs are made in the laboratory and can
bind targets in the body, e.g. TNF-α
Generic antibody structure:
Variable region
Fc portion
Fab portion
Designing a TNF-a inhibitor
- We take a MAB designed to bind TNF-α but only use the Fab portion – this makes the “biologic” molecule less immunogenic
- 2 x 20 KDa PEG chains linked to a lysine residue are attached to the Fab portion
What is Certolizumab pegol?
- Certolizumab pegol (Cimzia): PEGylated
monoclonal antibody fragment - The MAB is expressed in E. coli and then
processed to bioconjugate the Fab portion - This biological medicine (biologic) binds to TNF-α stopping its involvement in the inflammatory process
- Bioconjugation of the PEG moiety increases
the half-life of certolizumab pegol to 13 days
allowing a fortnightly maintenance dose
What are some other TNF-a inhibitors? (4)
What are biosimilar medicines?
- There are five other anti-TNF-a therapies available in the UK
- Adalimumab (Humira) – MAB
- Etanercept (Enbrel) – human dimeric fusion protein
- Golimumab (Simponi) – MAB
- Infliximab (Remicade) – MAB
- The innovator brand names are listed, but many “biosimilars” are now on the market
- Biosimilar medicines are biologics which are highly similar to another biologic already licensed
- Biologics are therefore different to generic small molecules which must be identical to the innovator
Other PEGylated protein drugs?
- There are currently 34 PEGylated drugs approved by the US FDA
- Some of the most important ones include:
- Filgrastim
- Asparaginase
- Interferon alpha/ beta
- Brain-derived neurotrophic factor (BDNF)
- Interleukin-6
- Filgrastim is PEGylated at the amino terminus and up to 4 lysine residues
- PEGylated filgrastim half-life is up to 4 times
longer than the non-PEGylated drug
Other PEGylated protein drugs:
What is gout?
Treatment of gout?
- Gout: type of arthritis that causes sudden attacks of severe pain/ swelling – uric acid crystals accumulate around joints
* Pegloticase (Krystexxa) is used to treat chronic gout in adults who have failed to respond to other therapies - Pegloticase is a PEGylated, recombinant
uricase, i.e. a protein drug - Tetramer with each unit containing 30 lysine AA residues
- 9 of the 30 residues (on each unit) are
PEGylated
PEGylated nanoparticles
- Nanoparticles are materials with overall dimensions at the nanoscale – typically said to be 1 nm to 100 nm
- Multiple uses in pharmaceutical science particularly as “carriers” of drugs or vaccines
- Nanocarriers suffer from the same
pharmacokinetic issues as protein drugs,
e.g. opsonisation, or removal by macrophages - Nanocarriers can be PEGylated in the same way that a protein drug would be
- Critical process in the development of the
Pfizer and Moderna mRNA COVID-19 vaccines
